Add Context7 remote MCP server to auto-generated config

Context7 provides up-to-date library documentation for LLMs via a
remote endpoint — no local binary needed. Always registered since it
has no PATH dependency.

Also switches generated config from .json to .jsonc so we can include
a comment about the optional API key for higher rate limits. The
existing-config check now detects both file extensions.

scripts/smoke-test.sh

@@ -160,11 +160,11 @@ else
 fi
 rm -f "$tmpout"
 
-# Config generation with anthropic provider writes valid JSON with the
+# Config generation with anthropic provider writes valid JSONC with the
 # expected shape. The script's log message goes to stderr (line 1 of
 # generate-config.py uses file=sys.stderr) so capturing only stdout
-# gives us clean JSON.
-label="generate-config produces valid opencode.json"
+# gives us clean JSONC. We strip // comments before validating JSON.
+label="generate-config produces valid opencode.jsonc"
 tmp=$(mktemp -d)
 if docker run --rm \
     -e OPENCODE_PROVIDER=anthropic \
@@ -173,24 +173,28 @@ if docker run --rm \
     "$IMAGE" sh -c '
       mkdir -p /tmp/home
       python3 /usr/local/lib/opencode-devbox/generate-config.py 2>/dev/null
-      cat /tmp/home/.config/opencode/opencode.json
-    ' > "$tmp/out.json" 2>/dev/null; then
+      cat /tmp/home/.config/opencode/opencode.jsonc
+    ' > "$tmp/out.jsonc" 2>/dev/null; then
+  # Strip single-line // comments for JSON validation
+  sed 's|//.*$||' "$tmp/out.jsonc" > "$tmp/out.json"
   if python3 -c "
 import json, sys
 c = json.load(open('$tmp/out.json'))
 assert c['model'].startswith('anthropic/'), c
 assert c['autoupdate'] is False
 assert c['share'] == 'disabled'
+assert 'context7' in c.get('mcp', {}), 'context7 MCP not registered'
 " 2>&1; then
     pass "$label"
   else
-    fail "$label: output doesn't match expected shape: $(cat "$tmp/out.json")"
+    fail "$label: output doesn't match expected shape: $(cat "$tmp/out.jsonc")"
   fi
 else
-  fail "$label: container failed: $(cat "$tmp/out.json")"
+  fail "$label: container failed: $(cat "$tmp/out.jsonc")"
 fi
 
 # Config generation is idempotent — running twice must not overwrite.
+# Tests both legacy .json and new .jsonc detection.
 label="generate-config never overwrites existing config"
 if docker run --rm \
     -e OPENCODE_PROVIDER=anthropic \